1. Field of the Invention
The invention relates to roll stands with multiple rolls for rolling strip-shaped roll stock, comprising a lower working roll and an upper working roll, support rolls correlated with each working roll, roll bending devices for the working rolls, as well as devices for advancing and balancing the support rolls, wherein the lower and the upper working rolls of the roll stand are supported in two lower, respectively, two upper support rolls which are arranged symmetrically to the vertical roll axis plane of the working rolls and are supported in pairs in lower and upper support roll insert parts.
2. Description of the Related Art
A roll stand with multiple rolls of this kind is known from JP 10 263 632 A.
The on-going improvement of environmental conditions, the scarcity of raw materials, and the requirement asked of the industry to produce components of different kinds with optimal, product-specific properties in a cost-effective manner, have resulted in the development of new manufacturing methods to which belongs the so-called "flexible rolling". Flexible rolling, in which the roll gap during the rolling process if controlled according to the thickness profile of a strip of roll stock changing over the strip length, makes a processing time-reducing manufacture of strip material possible whose thickness profile changes in the rolling direction as calculated, relating to a certain component and matched to the load situation. Such rolled strip manufactured of steel and non-iron metals is suitable for the lightweight construction in the automobile industry, air and space technology, and railroad car construction (DE-Z Fertigung, 1995, volume 23, issue 10, pp. 40-42).
While in conventional rolling it is desired to produce a flat strip that is as planar as possible and without profile changes along the entire strip length, in the flexible rolling process it is desired to produce controlled strip thickness changes over the strip length. The possible strip thickness reduction can be performed in a controlled fashion between a minimal reduction, which still maintains a stable rolling process, and a maximum reduction of more than 50%.
DE 195 18 144 A1 describes a rolling mill with working rolls which inherently carry the risk of horizontal bending during the rolling process because of their small roll diameter. In this rolling mill, the upper and the lower working rolls are driven, respectively, by a circumferential force, generated by the rolling force, of the rolling moments introduced into the support rolls. In a further multi-roll stand described also in DE 195 18 144 A1 the working rolls are supported by support roll pairs. The working rolls, which are accordingly guided along two contact lines relative to the support rolls, allow only a limited adjusting range for the working roll bending.
DE 22 06 912 C3 discloses a roll stand with two working rolls and oppositely displaceable intermediate rolls which can be adjusted to the width of the strip. They are respectively rotationally positioned in a support roll pair wherein the working rolls are provided with a roll bending device for improved adaptation to the strip profile. A disadvantage of this roll stand type for the application in flexible rolling is also the horizontal bending of the working rolls, the circumferential force transmitting the rolling moment, as well as the relatively large masses with respect to the required high acceleration properties of the roll advancement.
A further type of working roll support against horizontal bending by means of laterally arranged support rolls is described in EP 0 121 811 B1. However, this rolling mill concept without drive of the working rolls also does not provide an improvement of the rolling moments introduced into the working rolls.
Roll stands with multiple rolls according to EP 0 665 067 B1 comprise working rolls with smallest diameters and sufficient support, but require a considerable expenditure with respect to features for compensation of the bending of the roll set, such as support rolls and bending devices, and are limited with respect to the obtainable strip thickness reduction.
The positional changes required for flexible rolling in order to follow at all times the set-point strip length profile changes and the thus needed rolling force and rolling moment changes require a high dynamics of the roll advancement and the roll drive. On the one hand, a safe and no-slip transmission of the rolling moments onto the working rolls must be ensured; on the other hand, the accelerated controlled opening and closing of the rolling gap changes the pressing force between the support rolls and working roll. Moreover, the rolling force constantly changing during a reduction stage as a function of the thickness reduction results in a dynamic bending of the roll set.